When you're startled by a loud noise or sudden movement, you may jump a little bit. But for people with a condition called hyperekplexia, also called "startle disease," this reaction is so exaggerated that sufferers are often injured and even killed when they're surprised. It's also one cause of sudden infant death syndrome (SIDS). Now, researchers have discovered that the condition seems largely connected to one gene.

The disease is caused by multiple genetic mutations, the end result of which is a failure of nerve cells to properly communicate. Specifically, the mutations affect how a molecule called glycine is moved between cells.

Normally, glycine sends inhibitory signals, which dampen a person's responses to noise and sound. In people with startle disease, these inhibitory signals are not received, and the result is an amplified, harmful response.

In the new study, researchers at the University College London and Swansea University in Wales analyzed information from 93 patients with startle disease across the globe, and identified 19 new genetic mutations. The mutations were all in the genes that encode a protein called GlyT2, which is responsible for transporting glycine into cells.

For people who suffer from hyperekplexia, this could be a tremendous boon. Future therapies could target GlyT2, and help prevent anyone from ever being scared to death.